3.
= 2 sin (13π/12) cos(13π/12) = sin(2*(13π/12)) = sin(13π/6) =
2 2 2
= sin(2π+π/6) = sin(π/6) = 1 * 1 = 1/4 = 0.25
2 2 2 2
4.
a) = -19(cos² 84°-sin² 84°) = -19cos(2*84°) = -19
cos168° cos168°
б) = √8(cos² (13π/8) - sin² (13π/8))= √8 cos(2*(13π/8))=
= √8 cos(13π/4) = √8 cos(2π+π+π/4)= √8 cos(π+π/4)=
= √8 * (-cos (π/4)) = -√8 * √2 = -√16 = -4/2 = -2
2 2